HAHA, I think most if not all credit cards have that in their exclusion list already, even UOB One Card excludes Grabpay top-up already.
I would think you're much better off just paying directly with a credit card that has like 2/3% cashback. Grab points work out to only be about 0.08% rebate.
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Standard Chartered Unlimited Cashback Credit Card
Up to 1.5% on eligible spend
POSB Everyday Card
UOB One Card